1. Technical Field
The present invention relates to a surface light source, a method of driving the same, and a backlight unit having the same. In a more particular embodiment of the invention, a surface light source is capable of varying the brightness applied to individual portions of the area of a liquid crystal panel.
2. Discussion of Related Art
A liquid crystal display displays an image, using the electrical and optical properties of liquid crystal. The liquid crystal display is widely employed in portable computers, communication devices, liquid crystal television receivers, aerospace industry, and the like because volume and weight are smaller and lighter than those of a cathode ray tube (CRT).
The liquid crystal display includes a controlling unit to control a liquid crystal panel and a backlight source to illuminate the liquid crystal panel. The controlling unit includes pixel electrodes arranged on a first substrate, a common electrode disposed on a second substrate, and the liquid crystal panel disposed between the pixel electrodes and the common electrode. There are a plurality of pixel electrodes for each common electrode, to achieve a resolution of the liquid crystal display. The common electrode faces the pixel electrodes. Thin film transistors (TFT) are connected to the pixel electrodes to apply voltages of different levels thereto and a reference voltage of the same level is applied to the common electrode. The pixel electrodes and the common electrode are made of a transparent conductive material.
The light produced by the backlight source passes through the pixel electrodes, the liquid crystal panel, and the common electrode sequentially. In this case, the quality of an image transmitted through the liquid crystal panel significantly depends on the brightness of and uniformity of brightness of the backlight source. Generally, when the brightness and the uniformity of brightness are high, the image quality becomes high.
The backlight source of a conventional liquid crystal display typically employs a bar-shaped cold cathode fluorescent lamp (CCFL) or a dot-shaped light emitting diode (LED). The cold cathode fluorescent lamp has high brightness and long lifespan and generates less heat than an incandescent lamp. On the other hand, The LED has high power consumption, but has excellent brightness. Liquid crystal displays having a CCFL or an LED tend to suffer from nonuniform brightness. In order to increase the uniformity of brightness, the backlight source employing a CCFL or LED as a light source requires optical members, such as a light guide panel (LGP), a diffusion member, and a prism sheet. However, the optical members significantly increase the size and weight of a liquid crystal display employing the aforementioned CCFL or LED.
A flat fluorescent lamp (FFL) has been proposed as the backlight source of the liquid crystal display.
Referring to FIG. 1, a conventional surface light source 100 includes a light source body 110 and electrodes 160 provided at the outer surface of both lateral edges of the light source body 110. The light source body 110 includes first and second substrates facing each other by a predetermined distance. A plurality of partitions 140 are disposed between the first and second substrates to partition a space defined by the first and second substrates into plural discharging channels 120. A sealing member (not shown) is disposed at the rims of the first and second substrates to isolate the discharging channels 120 from the exterior. A discharge gas is injected into discharging spaces 150 in the discharging channels. In order to drive the surface light source to be discharged, an electrode is coated on the first and second substrates or on only one of the first and second substrates to have the same area per a discharging channel in the form of a minus-shaped band or an island electrode. Thus, all the channels discharge uniformly when the surface light source is driven by an inverter. In this way, the surface light source maintains a predetermined degree of brightness during the driving.